The present invention relates to a case for accommodating and transporting a photomask or a substrate for a photomask (hereinafter simply referred to as "photomask") to be used in the photolithography process for the manufacture of semiconductor devices such as LSI, ultra LSI, etc.
In the past, a photomask was accommodated directly in a case or accommodated and transported in a case using a buffer material of a polyvinyl chloride bag inflated by gas or a polyvinyl chloride bag containing sponge. Further, the photomask accommodated in a case was pressed down by providing a cushion material such as sponge within the upper lid of the case. As such cushion material, a material containing a moisture-resistant substance such as silica gel has been used due to differences in rinsing method of photomask or in sealing property of the case.
However, when the photomask is accommodated directly in a case, there is a free space between the case and the photomask which permits shaking or rattling during movement, and accordingly dust is generated during transportation. As a result, the photomask or a pellicle membrane covering the photomask (hereinafter referred to as "photomask pellicle") is contaminated. When the photomask is accommodated in a case using a polyvinyl chloride bag inflated by gas or a polyvinyl chloride bag as a buffer material containing a material such as sponge, the bag may be broken by impact during transport or foreign objects may spread in the bag. Further, when the case is opened, the polyvinyl chloride bag may not be held integrally with the upper lid of the case and may fall onto the photomask which is exposed at the upper portion of the case. As a result, a flaw or stain may be caused on the surface of the photomask or the photomask pellicle because of an inadequate seal between the upper lid and the polyvinyl chloride bag.
Also, when a cushion material such as sponge is provided, shaking of the photomask during transportation cannot be perfectly prevented because the cushion material is provided only in the upper lid of the case and it is in contact only with one side of the photomask, and similar problems occur due to dusting from the portions between the case bottom or case side and the photomask. Again, problems result when the cushion material falls out of the lid when the upper lid is opened or closed.